ˈside efˌfect BrE AmE noun [countable]
1 . an effect that a drug has on your body in addition to curing pain or illness
harmful/serious/adverse etc side effect
a natural remedy with no harmful side effects
side effect of
the side effects of the medication
2 . an unexpected or unplanned result of a situation or event:
These policy changes could have beneficial side effects for the whole economy.